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Full text of "The Flow Of Gases In Furnaces"

DESIGN OF OPEN-HEARTH FURNACES               291
The heat loss takes place continually during both the heating
and cooling cycles. This has suggested the possibility of recover-
ing a portion of this heat by enclosing the chambers, with an air
space all around them, in a sheet-iron housing arranged in such a
manner that the air supply for the furnace is drawn from the
highest and hottest portion of the enclosure. This housing should
provide sufficient room to permit the inspection of the chamber
walls.
All regenerative furnaces are more or less subject to explosions
at reversal. These explosions crack and otherwise damage the
brickwork, producing air leakage which reduces the temperature
of the waste gases and increases their volume. The effect of this
leakage is intensified when a strong draft must be used to pull the
waste gases out of the furnace. The intensity of the draft depres-
sion increases progressively from the port to the base of the stack;
and the seriousness of the air infiltration necessarily increases
as the draft depression increases, the greatest amount of air
entering the system through the walls of the flues leading to the
chimney. Leakage outward undoubtedly occurs with both the
air and the gas; but, as the pressure within the flues is extremely
low, the volume lost is much less than the infiltration through the
same wall. The only way of preventing air from leaking into the
flues is to provide them with a covering of sheet steel of suitable
thickness. This will, at the same time, necessitate a consideration
of the fact that an explosion within a tight casing may be much
more violent than one occurring in a brick flue. Such a casing
and the heat insulation of these flues will increase considerably
the amount of heat available for the generation of steam.
One of the factors brought out in the preceding computation
was the draft depression necessary to pull a proportionate amount
of the waste gases through the gas-port of the furnace. This
indicates that a better-working furnace would result from having
large uptakes through which the waste gases would pass with a
low velocity down to the cinder pockets. A further advantage                          
resulting from this increase in uptake area on the outgoing end
will be a greatly increased efficiency of the cinder pocket in                          t
catching cinder and other material which is carried out of the
furnace and thus increasing the life of the regenerators. The
carrying power of a flowing stream varies as the sixth power of
its velocity. That is, when the velocity is doubled, the weight of